I live in Wyoming and the seasons here are Summer, Almost Winter, Winter, and Still Winter. (snowed early September last year and it snowed again for my birthday...in JUNE!)

For your coat, look at your zipper. Chances are it's a YKK zipper or will fit one. I just made a rectangle out of some quilted fabric sold at Walmart and sewed a side of the appropriate sized YKK zipper on both sides so that it could zip to my coat. I got kind of fancy and sewed elastic at the top and under my boobs to make it fitted. Voila instant maternity/baby-wearing coat for less than $10.

I donated it or threw it away already sometime in the summer. And it was those huge poofy kinds. Yuck. We're just going to have to dig more money out of savings from tax return last year to buy me a maternity coat.

I bought my winter coats this past summer! I think I was about 6weeks along. LOL! The everyday casual one I bought from ebay and then I found a nice wool peacoat on clearance from Motherhood Maternity. I felt silly buying winter coats in July, but we just had our first snowstorm here this weekend so now I am so glad that I did.

Maybe eBay? I bet there are quite a lot of women who bought maternity coats and want to sell them now they're done with their pregnancy(ies). They're not cheap, so it makes sense to sell them (or perhaps if you buy a new one you could resell it for half the cost?)

H&M had some decently priced ones in the maternity section when I was there, I think. I didn't pay them much attention though.

I live in Ottawa, and have moved around Canada quite a bit so I know the need for a good warm coat in our climate!
I ended up buying a black wool maternity coat from Thyme that is really cute (I got the "wrap" 2 button version but there is also a 4 button one). I did have a coupon for 50% (originally $129) off so that helped a lot. I also happen to know a tailor who can take it in for me after the pregnancy if needed. The one I got lays pretty nice because I can wrap it as much as I want, so I'm not sure if I will even have to bother taking it in. For boots I have wool lined mukluks that are easy to slip on, freaking adorable and sooo comfy (very pricey at $300, but an investment piece because I pretty much live in them) I wore them last winter without any issues, but for added safety I have STABILicers Traction Device ($20 from Mountain Equipment Coop) to slip over the sole on icy days. You can always try to get some of your money back selling your winter gear to new moms next year.